The dual peroxisome proliferator-activated receptor alpha/gamma activator muraglitazar prevents the natural progression of diabetes in db/db mice

There are two major defects in type 2 diabetes: 1) insulin resistance and 2) insulin deficiency due to loss of beta-cell function. Here we demonstrated that treatment with muraglitazar (a dual peroxisome proliferator-activated receptor alpha/gamma activator), when initiated before or after the onset of diabetes in mice, is effective against both defects. In study 1, prediabetic db/db mice were treated for 12 weeks. The control mice developed diabetes, as evidenced by hyperglycemia, hyperinsulinemia, reduced insulin levels in the pancreas, blunted insulin response to glucose, and impaired glucose tolerance. The muraglitazar-treated mice had normal plasma glucose, and insulin levels, equivalent or higher pancreatic insulin content than normal mice, showed a robust insulin response to glucose and exhibited greater glucose tolerance. In study 2, diabetic db/db mice were treated for 4 weeks. The control mice displayed increased glucose levels, severe loss of islets, and their isolated islets secreted reduced amounts of insulin in response to glucose and exendin-4 compared with baseline. In muraglitazar-treated mice, glucose levels were reduced to normal. These mice showed reduced loss of islets, and their isolated islets secreted insulin at levels comparable to baseline. Thus, muraglitazar treatment decreased both insulin resistance and preserved beta-cell function. As a result, muraglitazar treatment, when initiated before the onset of diabetes, prevented development of diabetes and, when initiated after the onset of diabetes, prevented worsening of diabetes in db/db mice.     

Hypoplasia of pancreatic islets in transgenic mice expressing activin receptor mutants.

Activin, a member of the TGF-beta superfamily, regulates the growth and differentiation of a variety of cell types. Based on the expression of activin in pancreatic rudiments of rat embryos and stimulation of insulin secretion from adult rat pancreatic islets by activin, activin is implicated in the development and function of islets. To examine the significance of activin signaling in the fetal and postnatal development of islets, transgenic mice expressing a dominant negative form of activin receptor (dn-ActR) or a constitutively active form of activin receptor (ActR-T206D) in islets were generated together with the transgenic mice expressing intact activin receptor (intact ActR) as a negative control. Transgenic mice with both dn-ActR and ActR-T206D showed lower survival rates, smaller islet area, and lower insulin content in the whole pancreas with impaired glucose tolerance when compared with transgenic mice with intact ActR or littermates, but they showed the same alpha cell/beta cell ratios as their littermates. In addition to islet hypoplasia, the insulin response to glucose was severely impaired in dn-ActR transgenic mice. It is suggested that a precisely regulated intensity of activin signaling is necessary for the normal development of islets at the stage before differentiation into alpha and beta cells, and that activin plays a role in the postnatal functional maturation of islet beta cells.     

Overexpression of pituitary adenylate cyclase-activating polypeptide in islets inhibits hyperinsulinemia and islet hyperplasia in agouti yellow mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an intraislet neuropeptide and shares insulinotropic and insulin-sensitizing properties with glucagon-like peptide-1 (GLP-1); however, the pathophysiological significance of PACAP in diabetes remains largely unknown. To assess this, we crossed our recently developed transgenic mice overexpressing PACAP in pancreatic beta-cells (Tg/+), with lethal yellow agouti (KKA(y)) mice (A(y)/+), a genetic model for obesity-diabetes, and examined the metabolic and morphological phenotypes of F(1) animals. Tg/+ mice with the A(y) allele (Tg/+:A(y)/+) developed maturity-onset obesity and diabetes associated with hyperglycemia, hyperlipidemia, and hyperphagia, similar to those of A(y)/+ mice, but hyperinsulinemia was significantly ameliorated in Tg/+:A(y)/+ mice. Although A(y)/+ mice exhibited a marked increase in islet mass resulting from hyperplasia and hypertrophy, this increase was significantly attenuated in Tg/+:A(y)/+ mice. Size frequency distribution analysis revealed that the very large islets comprising one-fourth of islets of A(y)/+ mice were selectively reduced in Tg/+:A(y)/+ mice. Because functional defects have been demonstrated in the large islets of obese animal models, together these findings suggest that PACAP regulates hyperinsulinemia and the abnormal increase in islet mass that occurs during the diabetic process.     

Beta cell expression of IGF-I leads to recovery from type 1 diabetes

Patients with type 1 diabetes are identified after the onset of the disease, when beta cell destruction is almost complete. beta cell regeneration from islet cell precursors might reverse this disease, but factors that can induce beta cell neogenesis and replication and prevent a new round of autoimmune destruction remain to be identified. Here we show that expression of IGF-I in beta cells of transgenic mice (in both C57BL/6-SJL and CD-1 genetic backgrounds) counteracts cytotoxicity and insulitis after treatment with multiple low doses of streptozotocin (STZ). STZ-treated nontransgenic mice developed high hyperglycemia and hypoinsulinemia, lost body weight, and died. In contrast, STZ-treated C57BL/6-SJL transgenic mice showed mild hyperglycemia for about 1 month, after which they normalized glycemia and survived. After STZ treatment, all CD-1 mice developed high hyperglycemia, hypoinsulinemia, polydipsia, and polyphagia. However, STZ-treated CD-1 transgenic mice gradually normalized all metabolic parameters and survived. beta cell mass increased in parallel as a result of neogenesis and beta cell replication. Thus, our results indicate that local expression of IGF-I in beta cells regenerates pancreatic islets and counteracts type 1 diabetes, suggesting that IGF-I gene transfer to the pancreas might be a suitable therapy for this disease.     

Insulin receptor substrate 2 plays a crucial role in beta cells and the hypothalamus

We previously demonstrated that insulin receptor substrate 2 (Irs2) KO mice develop diabetes associated with hepatic insulin resistance, lack of compensatory beta cell hyperplasia, and leptin resistance. To more precisely determine the roles of Irs2 in beta cells and the hypothalamus, we generated beta cell-specific Irs2 KO and hypothalamus-specific Irs2 knockdown (betaHT-IRS2) mice. Expression of Irs2 mRNA was reduced by approximately 90% in pancreatic islets and was markedly reduced in the arcuate nucleus of the hypothalamus. By contrast, Irs2 expression in liver, muscle, and adipose tissue of betaHT-IRS2 mice was indistinguishable from that of control mice. The betaHT-IRS2 mice displayed obesity and leptin resistance. At 4 weeks of age, the betaHT-IRS2 mice showed normal insulin sensitivity, but at 8 and 12 weeks, they were insulin resistant with progressive obesity. Despite their normal insulin sensitivity at 8 weeks with caloric restriction, the betaHT-IRS2 mice exhibited glucose intolerance and impaired glucose-induced insulin secretion. beta Cell mass and beta cell proliferation in the betaHT-IRS2 mice were reduced significantly at 8 and 12 weeks but not at 10 days. Insulin secretion, normalized by cell number per islet, was significantly increased at high glucose concentrations in the betaHT-IRS2 mice. We conclude that, in beta cells and the hypothalamus, Irs2 is crucially involved in the regulation of beta cell mass and leptin sensitivity.     

Hyperglycemia-induced B cell toxicity. The fate of pancreatic islets transplanted into diabetic mice is dependent on their genetic background.

The role of pancreatic B cell dysfunction in the phase preceding clinical onset of insulin-dependent and non-insulin-dependent diabetes mellitus has been much debated. In this investigation, the impact of a prolonged diabetic environment on pancreatic islet B cells transplanted syngeneically under the kidney capsule of C57BL/6 (B6) and C57BL/Ks (BKs) mice was studied. Alloxan-diabetic mice bearing a subcapsular islet graft insufficient to normalize the blood glucose level were rendered normoglycemic by a second intrasplenic islet graft after various period of hyperglycemia to examine the reversibility of hyperglycemia-induced B cell dysfunction. Using a perfusion technique of the graft-bearing, it was found that both strains of mice exhibited a diminished glucose-induced insulin secretion after 6 wk of hyperglycemia, when compared with normoglycemic mice carrying islet grafts. When normoglycemia was restituted by the splenic graft after 4 or 12 wk, there was a normalization of glucose-stimulated insulin secretion in the renal islet grafts in B6 mice, whereas insulin secretion from the grafted BKs islets remained impaired. Morphometric measurements of the islet grafts demonstrated a 50% reduction in the graft volume in diabetic BKs mice after 12 wk, compared with normoglycemic animals, whereas no such decrease was observed in B6 mice. Islet grafts removed from hyperglycemic mice of both strains exhibited diminished insulin mRNA contents, and in the BKs mice there was also a reduced glucose oxidation rate in the islet grafts in vitro. This metabolic dysfunction can only partly be explained by a reduced graft size. The present findings emphasize the genetic constitution as a decisive factor for the survival and function during a period of sustained stress on a limited B cell mass.     

Resistance to type 1 diabetes induction in 12-lipoxygenase knockout mice

Leukocyte 12-lipoxygenase (12-LO) gene expression in pancreatic beta cells is upregulated by cytotoxic cytokines like IL-1beta. Recent studies have demonstrated that 12-LO inhibitors can prevent glutamate-induced neuronal cell death when intracellular glutathione stores are depleted. Therefore, 12-LO pathway inhibition may prevent beta-cell cytotoxicity. To evaluate the role of 12-LO gene expression in immune-mediated islet destruction, we used 12-LO knockout (12-LO KO) mice. Male homozygous 12-LO KO mice and control C57BL/6 mice received 5 consecutive daily injections of low-dose streptozotocin to induce immune-mediated diabetes. Fasting serum glucose and insulin levels were measured at 7-day intervals, and the mice were followed up for 28 days. 12-LO KO mice were highly resistant to diabetes development compared with control mice and had higher serum insulin levels on day 28. Isolated pancreatic islets were treated with IL-1beta, TNF-alpha, and IFN-gamma for 18 hours. Glucose-stimulated insulin secretion in cytokine-treated islets from C57/BL6 mice decreased 54% from that of untreated islets. In marked contrast, the same cytokine mix led to only a 26% decrease in islets from 12-LO KO mice. Furthermore, cytokine-induced 12-hydroxyeicosatetraenoic acid (12-HETE) production was absent in 12-LO KO islets but present in C57/BL6 islets. Isolated peritoneal macrophages were stimulated for 48 hours with IFN-gamma + LPS and compared for nitrate/nitrite generation. 12-LO KO macrophages generated 50% less nitrate/nitrite when compared with C57BL/6 macrophages. In summary, elimination of leukocyte 12-LO in mice ameliorates low dose streptozotocin-induced diabetes by increasing islet resistance to cytokines and decreasing macrophage production of nitric oxide.     

In situ glucose uptake and glucokinase activity of pancreatic islets in diabetic and obese rodents.

The present study evaluated the involvement of glucose transport and phosphorylation in glucose-stimulated insulin release from pancreatic islets. Using quantitative histochemical techniques, we investigated basal islet glucose content, islet glucose uptake in situ during acute extreme experimental hyperglycemia, and islet glucokinase activity in several animal models of diabetes and obesity. The basal islet glucose content in anaesthetized diabetic or obese rodents was either the same or higher than that in their relevant controls. The rate of glucose uptake of islet tissue in these animals after an i.v. glucose injection was different. The db+/db+ mouse and the obese Zucker rat exhibited significantly reduced islet glucose uptake rates. RIP-cHras transgenic mice, BHE/cdb rats and partially pancreatectomized rats showed normal islet glucose uptake rates. The activity of islet glucokinase was increased to a different degree related to the blood glucose level. All five animal models of diabetes or obesity exhibited either a delay or a reduction of insulin release in response to supra maximal glucose stimulation. Our results indicate that the impairment of glucose-induced insulin release in diabetes is not consistently associated with a reduction of islet glucose uptake nor a change of glucokinase activity.     

微胶珠化胰岛肌肉内移植治疗小鼠1型糖尿病

背景：前期实验证明海藻酸钡微胶珠具有免疫隔离作用,并且不会引起免疫排斥反应。目的：观察包裹胰岛海藻酸钡微胶珠对1型糖尿病小鼠的治疗作用。方法：分离纯化SD大鼠胰腺单个胰岛细胞团,并包裹于海藻酸钡微胶珠内。以腹腔注射链脲佐菌素诱导建立C57BL／6小鼠1型糖尿病模型,随机分组：实验组小鼠股二头肌内多点注射包裹胰岛的海藻酸钡微胶珠,对照组小鼠股二头肌内多点注射胰岛,糖尿病对照组及正常对照组小鼠股二头肌内多点注射生理盐水。术后观察小鼠血糖及胰岛微胶珠在肌肉内存在状况。结果与结论：分离纯化后获得高纯度胰岛,每只供体可获得（905．4：1：34．5）个,并具有良好生物活性。实验组小鼠血糖降为正常的时间约为6．3d,移植胰岛存活时间大于30d,对照组小鼠血糖一直未降至正常,移植胰岛存活时间约为4d。实验组降糖速率明显快于对照组和糖尿病对照组（P〈0．05）。表明包裹胰岛的海藻酸钡微胶珠镶嵌在肌肉组织中可良好存活,治疗小鼠1型糖尿病。     

Disruption of leptin receptor expression in the pancreas directly affects beta cell growth and function in mice

Obesity is characterized by hyperinsulinemia, hyperleptinemia, and an increase in islet volume. While the mechanisms that hasten the onset of diabetes in obese individuals are not known, it is possible that the adipose-derived hormone leptin plays a role. In addition to its central actions, leptin exerts biological effects by acting in peripheral tissues including the endocrine pancreas. To explore the impact of disrupting leptin signaling in the pancreas on beta cell growth and/or function, we created pancreas-specific leptin receptor (ObR) KOs using mice expressing Cre recombinase under the control of the pancreatic and duodenal homeobox 1 (Pdx1) promoter. The KOs exhibited improved glucose tolerance due to enhanced early-phase insulin secretion, and a greater beta cell mass secondary to increased beta cell size and enhanced expression and phosphorylation of p70S6K. Similar effects on p70S6K were observed in MIN6 beta cells with knockdown of the ObR gene, suggesting crosstalk between leptin and insulin signaling pathways. Surprisingly, challenging the KOs with a high-fat diet led to attenuated acute insulin secretory response to glucose, poor compensatory islet growth, and glucose intolerance. Together, these data provide direct genetic evidence, from a unique mouse model lacking ObRs only in the pancreas, for a critical role for leptin signaling in islet biology and suggest that altered leptin action in islets is one factor that contributes to obesity-associated diabetes.     

Reversal of beta-cell suppression in vitro in pancreatic islets isolated from nonobese diabetic mice during the phase preceding insulin-dependent diabetes mellitus.

Insulin-dependent diabetes mellitus (IDDM) is characterized by a progressive autoimmune destruction of the pancreatic beta-cells. One of the best-suited animal models for IDDM is the nonobese diabetic (NOD) mouse. In this investigation pancreatic islets were isolated from female NOD mice aged 5-7, 8-11, and 12-13 wk and examined immediately (day 0) or after 7 d of culture (day 7). The mice showed a progressive disturbance in glucose tolerance with age, and a correspondingly increased frequency of pancreatic insulitis. Islets isolated from the oldest mice often contained inflammatory cells on day 0, which resulted in an elevated islet DNA content. During culture these islets became depleted of infiltrating cells and the DNA content of the islets decreased on day 7. Islets of the eldest mice failed to respond with insulin secretion to high glucose, whereas a response was observed in the other groups. After culture all groups of islets showed a markedly improved insulin secretion. Islets from the 12-13-wk-old mice displayed a lower glucose oxidation rate at 16.7 mM glucose on day 0 compared with day 7. Islet (pro)insulin and total protein biosynthesis was essentially unaffected. In conclusion, islets obtained from 12-13-wk-old NOD mice exhibit an impaired glucose metabolism, which may explain the suppressed insulin secretion observed immediately after isolation. This inhibition of beta-cell function can be reversed in vitro. Thus, there may be a stage during development of IDDM when beta-cell destruction can be counteracted and beta-cell function restored, provided the immune aggression is arrested.     

Ghrelin is a physiological regulator of insulin release in pancreatic islets and glucose homeostasis

Ghrelin, an acylated 28-amino acid peptide, was isolated from the stomach as the endogenous ligand for the growth hormone (GH) secretagogue receptor (GHS-R). Circulating ghrelin is produced predominantly in the oxyntic mucosa of stomach. Ghrelin potently stimulates GH release and feeding, and exhibits positive cardiovascular effects, suggesting a possible clinical application. Low plasma ghrelin levels are associated with elevated fasting insulin levels and insulin resistance, suggesting both physiological and pathophysiological roles for ghrelin in glucose metabolism. Here, we review the physiological role of ghrelin in the regulation of insulin release and glucose metabolism, and a potential therapeutic avenue to treat type 2 diabetes by manipulating ghrelin and/or its signaling. Ghrelin inhibits insulin release in mice, rats and humans. The signal transduction mechanisms of ghrelin in islet β-cells are distinct from those utilized in GH-releasing and/or GHS-R-expressing cells. Ghrelin is expressed in pancreatic islets and released into pancreatic microcirculations. Pharmacological and genetic blockades of islet-derived ghrelin markedly augment glucose-induced insulin release in vitro. In high-fat diet-induced mildly obese mice, ghrelin-deficiency enhances insulin release and prevents impaired glucose tolerance. Thus, manipulation of insulinostatic function of ghrelin — GHS-R system, particularly that in islets, could optimize the amount of insulin release to meet the systemic demand, providing a potential therapeutic application to prevent type 2 diabetes.     

Pancreatic gastrin stimulates islet differentiation of transforming growth factor alpha-induced ductular precursor cells.

Gastrin is transiently expressed in fetal islets during a critical period of their development from protodifferentiated islet precursors in fetal pancreatic ducts. To examine the possible role of gastrin as an islet cell growth factor, postnatal islet growth was studied in transgenic mice which overexpress gastrin and TGF alpha in their pancreas. Overexpression of a TGF alpha transgene causes metaplastic ductules containing numerous insulin expressing cells that resemble protodifferentiated precursors of the fetal pancreas. However, islet mass of the TGF alpha transgenic mice was not increased. Pancreatic overexpression of gastrin from a chimeric insulin/gastrin transgene transcribed from the insulin promoter markedly decreased the TGF alpha-stimulated increase in pancreatic duct mass. Furthermore, pancreatic coexpression of both gastrin and TGF alpha significantly increased islet mass in mice expressing both transgenes. These findings indicate that TGF alpha and gastrin can act synergistically to stimulate islet growth, although neither peptide alone is sufficient. Islet growth may possibly be stimulated through gastrin promoting the differentiation of insulin-positive cells in the TGF alpha-induced metaplastic ducts. This transgenic study suggests that islet neogenesis can be reactivated in the ductular epithelium of the adult pancreas by local expression of two growth factors, gastrin and TGF alpha.     

Cyclic adenosine monophosphate prevents the glucocorticoid-mediated inhibition of insulin gene expression in rodent islet cells.

Dexamethasone negatively regulates insulin gene expression in HIT-15 cells. In vivo, however, an excess of glucocorticoids results in an increase in insulin biosynthesis and peripheral hyperinsulinemia. To resolve this contradiction, we have studied the effects of dexamethasone in primary rat islet cells. We show here that dexamethasone decreases insulin mRNA levels in single islet cells, as in HIT-15 cells, but does not affect these levels in reaggregated islet cells and increases them in intact islets of Langerhans. Because cAMP is an important regulator of insulin gene expression and intracellular cAMP content may be decreased in single beta cells, we investigated whether cAMP could prevent the inhibitory effect of dexamethasone on insulin mRNA levels. In the presence of cAMP analogues, the inhibitory action of dexamethasone was not only prevented, but insulin mRNA increased to levels comparable to those observed when cAMP analogues were used alone. We conclude that the insulin gene is negatively regulated by dexamethasone in single islet cells, but that other factors such as cAMP prevent this effect when the native environment of islet cells is preserved. Our results indicate that insulin gene regulation is influenced by cell to cell contacts within the islet, and that intracellular cAMP levels might be influential in this regulation.     

Mapping of murine diabetogenic gene mody on chromosome 7 at D7Mit258 and its involvement in pancreatic islet and beta cell development during the perinatal period.

Mutation of the murine maturity-onset diabetes mellitus of the young (Mody) locus induces diabetes, but the effects of its homozygosity on the pancreas remain unknown. F2 mice were obtained by F1 (diabetic C57BL6 x normal Mus musculus castaneus) crosses. About 20% of the F2 progeny developed diabetes by 2 wk of age, 50% of the progeny were normal at 2 wk and developed diabetes between 5 and 8 wk of age, and the remaining 30% did not develop diabetes. Quantitative trait locus analysis using blood glucose levels of 118 F2 mice at 2 wk of age and 5-8 wk of age located Mody within 3 cM of D7Mit258. Histopathological investigation revealed hypoplastic islets (approximately 33% of that of wild-type mice) and a lower density of beta cells (approximately 20% of wild-type) with a reciprocal dominance of alpha cells (four times that of wild-type) in Mody homozygotes. Electron microscopic observations revealed a specific decrease in the number of insulin secretory granules and a lower density of beta cells. Ratios of insulin to glucagon contents confirmed specific decreases in insulin content: 0.01 for homozygotes, 0.54 for heterozygotes, and 1.11 for wild-type mice on day 14. These results suggest that Mody is involved in both islet growth and beta cell function.     

Pancreatic expression of interleukin-4 abrogates insulitis and autoimmune diabetes in nonobese diabetic (NOD) mice

Diabetes in nonobese diabetic (NOD) mice is a T cell-dependent autoimmune disease. The destructive activities of autoreactive T cells have been shown to be tightly regulated by effector molecules. In particular, T helper (Th) 1 cytokines have been linked to diabetes pathogenesis, whereas Th2 cytokines and the cells that release them have been postulated to be protective from disease. To test this hypothesis, we generated transgenic NOD mice that express interleukin (IL) 4 in their pancreatic beta cells under the control of the human insulin promoter. We found that transgenic NOD-IL-4 mice, both females and males, were completely protected from insulitis and diabetes. Induction of functional tolerance to islet antigens in these mice was indicated by their inability to reject syngeneic pancreatic islets and the failure of diabetogenic spleen cells to induce diabetes in transgenic NOD-IL-4 recipients. Interestingly, however, islet expression of IL-4 was incapable of preventing islet rejection in overtly diabetic NOD recipient mice. These results demonstrate that the Th2 cytokine IL-4 can prevent the development of autoimmunity and destructive autoreactivity in the NOD mouse. Its ability to regulate the disease process in the periphery also indicates that autoimmune diabetes in NOD mice is not a systemic disease, and it can be modulated from the islet compartment.     

Increased islet apoptosis in Pdx1+/- mice

Mice with 50% Pdx1, a homeobox gene critical for pancreatic development, had worsening glucose tolerance with age and reduced insulin release in response to glucose, KCl, and arginine from the perfused pancreas. Surprisingly, insulin secretion in perifusion or static incubation experiments in response to glucose and other secretagogues was similar in islets isolated from Pdx1(+/-) mice compared with Pdx1(+/+) littermate controls. Glucose sensing and islet Ca(2+) responses were also normal. Depolarization-evoked exocytosis and Ca(2+) currents in single Pdx1(+/-) cells were not different from controls, arguing against a ubiquitous beta cell stimulus-secretion coupling defect. However, isolated Pdx1(+/-) islets and dispersed beta cells were significantly more susceptible to apoptosis at basal glucose concentrations than Pdx1(+/+) islets. Bcl(XL) and Bcl-2 expression were reduced in Pdx1(+/-) islets. In vivo, increased apoptosis was associated with abnormal islet architecture, positive TUNEL, active caspase-3, and lymphocyte infiltration. Although similar in young mice, both beta cell mass and islet number failed to increase with age and were approximately 50% less than controls by one year. These results suggest that an increase in apoptosis, with abnormal regulation of islet number and beta cell mass, represents a key mechanism whereby partial PDX1 deficiency leads to an organ-level defect in insulin secretion and diabetes.     

In vivo evidence for the contribution of human histocompatibility leukocyte antigen (HLA)-DQ molecules to the development of diabetes

Although DQA1*0301/DQB1*0302 is the human histocompatibility leukocyte antigen (HLA) class II gene most commonly associated with human type 1 diabetes, direct in vivo experimental evidence for its diabetogenic role is lacking. Therefore, we generated C57BL/6 transgenic mice that bear this molecule and do not express mouse major histocompatibility complex (MHC) class II molecules (DQ8(+)/mII(-)). They did not develop insulitis or spontaneous diabetes. However, when DQ8(+)/mII(-) mice were bred with C57BL/6 mice expressing costimulatory molecule B7-1 on beta cells (which normally do not develop diabetes), 81% of the DQ8(+)/mII(-)/B7-1(+) mice developed spontaneous diabetes. The diabetes was accompanied by severe insulitis composed of both T cells (CD4(+) and CD8(+)) and B cells. T cells from the diabetic mice secreted large amounts of interferon gamma, but not interleukin 4, in response to DQ8(+) islets and the putative islet autoantigens, insulin and glutamic acid decarboxylase (GAD). Diabetes could also be adoptively transferred to irradiated nondiabetic DQ8(+)/mII(-)/B7-1(+) mice. In striking contrast, none of the transgenic mice in which the diabetes protective allele (DQA1*0103/DQB1*0601, DQ6 for short) was substituted for mouse MHC class II molecules but remained for the expression of B7-1 on pancreatic beta cells (DQ6(+)/mII(-)/B7-1(+)) developed diabetes. Only 7% of DQ(-)/mII(-)/B7-1(+) mice developed diabetes at an older age, and none of the DQ(-)/mII(+)/B7-1(+) mice or DQ8(+)/mII(+)/B7-1(+) mice developed diabetes. In conclusion, substitution of HLA-DQA1*0301/DQB1*0302, but not HLA-DQA1*0103/DQB1*0601, for murine MHC class II provokes autoimmune diabetes in non-diabetes-prone rat insulin promoter (RIP).B7-1 C57BL/6 mice. Our data provide direct in vivo evidence for the diabetogenic effect of this human MHC class II molecule and a unique "humanized" animal model of spontaneous diabetes.     

PKClambda regulates glucose-induced insulin secretion through modulation of gene expression in pancreatic beta cells

Altered regulation of insulin secretion by glucose is characteristic of individuals with type 2 diabetes mellitus, although the mechanisms that underlie this change remain unclear. We have now generated mice that lack the lambda isoform of PKC in pancreatic beta cells (betaPKClambda(-/-) mice) and show that these animals manifest impaired glucose tolerance and hypoinsulinemia. Furthermore, insulin secretion in response to high concentrations of glucose was impaired, whereas the basal rate of insulin release was increased, in islets isolated from betaPKClambda(-/-) mice. Neither the beta cell mass nor the islet insulin content of betaPKClambda(-/-) mice differed from that of control mice, however. The abundance of mRNAs for Glut2 and HNF3beta was reduced in islets of betaPKClambda(-/-) mice, and the expression of genes regulated by HNF3beta was also affected (that of Sur1 and Kir6.2 genes was reduced, whereas that of hexokinase 1 and hexokinase 2 genes was increased). Normalization of HNF3beta expression by infection of islets from betaPKClambda(-/-) mice with an adenoviral vector significantly reversed the defect in glucose-stimulated insulin secretion. These results indicate that PKClambda plays a prominent role in regulation of glucose-induced insulin secretion by modulating the expression of genes important for beta cell function.